1. Field of the Invention
This invention relates to a winding reel for magnetic tape to be accommodated in a magnetic tape cartridge for use. More particularly, it is concerned with the winding reel for the magnetic tape which can be suitably used in the magnetic tape cartridge for VTR (video tape recorder), in particular.
2. Description of the Prior Art
The conventional magnetic tape cartridge is constructed in such a manner that upper and lower half cases shaped from a plastic material are joined together to form a closed space inside it, and a pair of reels for feeding and winding (or taking-up) the magnetic tape are fitted in the internal cavity formed by the upper and lower half cases as joined together, and a magnetic tape is wound on and extended between these reels.
FIG. 1 of the accompanying drawing illustrates one embodiment of the internal structure of the conventional magnetic tape cartridge for VTR, in which the upper half case of the magnetic tape cartridge is shown to have been removed. As illustrated in the drawing, the magnetic tape cartridge is so constructed that a feeding reel 4 and a winding reel 6 are disposed in the lower half case 2, and a magnetic tape T is guided from the feeding reel 4 to the take-up reel 6 through tape guides 8, 10, 12 and 14 for tape feeding.
In the meantime, the conventional feeding reel 4 and the take-up reel 6 are of the same construction as shown, for example, in FIGS. 2 and 3. In more detail, the reels 4 and 6 each include the lower flange 22 of a synthetic resin material with a reel drum 20, on which the magnetic tape T is wound, being integrally formed therewith, and the upper flange 26 joined to the end face 24 of the abovementioned reel drum 20 in confrontation to the lower flange 22. While the upper flange 26 and the reel drum 20 can be joined by various well known methods, it is preferable that, as shown in the drawing, a plurality of projections 28 are provided on the end face 24 of the reel drum 20, and they are fitted in holes 30 formed at corresponding positions in the upper flange 26 to pass therethrough so as to be protruded from the holes 30. Then, these projections are melted to fixedly secure the upper flange 26 to the reel drum 20. In addition, a center boss 32 is fixedly provided at the center position of the reel drum 20 in a manner to project from the top surface of the upper flange 26. The center boss 32 is to define a rotational axis of the reel in cooperation with an external drive shaft receiving socket (not shown in the drawing) formed by drilling a hole in the reel drum 20 from the other end of the reel drum 20 along its center axis. Further, in the embodimental reel, a dovetail groove 34 is formed in one outer peripheral part of the reel drum 20. In this dovetail groove 34, there is fitted a clamp 36 having an outer peripheral surface to define the entire circumference thereof in cooperation with the reel drum 20. Both dovetail groove 34 and the clamp 36 serve to fasten the leading edge of the magnetic tape T to the reel drum 20, as shown in FIG. 3.
In the conventional magnetic tape cartridge 1 of such construction, since the feeding reel 2 and the take-up reel 4 are in exactly the same shape and size as mentioned in the foregoing, it is not required to assemble the feeding reel 2 and the take-up reel 4 by making distinction between them. As the results of various researches and experiments, however, it was discovered that, by making the reel drum 20 broader than that of the feeding reel 4, it becomes possible to remarkably reduce possible damage to the magnetic tape, and to prolong use of the tape over a long period of time. On account of this, the feeding reel 4 and the take-up reel 6 have been so manufactured that only the breadth of the reel drum 20 may become different. As the consequence of this, for both the feeding reel 4 and the take-up reel 6 it has become necessary to distinguish them from each other at the time of their assembly.